The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engine operation involves combustion that generates exhaust gas. During combustion, an air/fuel mixture is delivered through an intake valve to cylinders and is combusted in the cylinders. After combustion, a piston forces the exhaust gas in the cylinders through an exhaust valve and into an exhaust system. The exhaust gas may contain emissions such as oxides of nitrogen (NOx) and carbon monoxide (CO).
Exhaust treatment systems monitor and treat the exhaust gas to meet emissions requirements. Treatment of exhaust gas may include the use of particulate filters, catalysts such as diesel oxidation catalysts (DOC) and/or selective catalytic reduction (SCR) catalysts, hydrocarbon injection and/or other devices. The efficiency of the SCR catalyst is usually monitored to ensure that emission levels remain acceptable during operation.